In recent years, small portable devices, such as mobile phones, equipped with an image pickup device (camera module) have become widely popular, and taking pictures instantly with such small portable devices has become a common practice. For small image pickup devices incorporated in such a small portable device, an image pickup lens composed of four lenses is proposed (see Patent Document 1, for example). This image pickup lens is compact, has a small full open F number and allows an image surface to be flat from the center to the periphery. At the same time, the image pickup lens has high image quality.
The image pickup lens described in Patent Document 1 includes, in order from the object side to the image surface side: an aperture stop, a first lens that is a biconvex lens having positive refractive power; a second lens that is a negative meniscus lens having negative refractive power and whose lens surface facing the object side is convex; a third lens that is a positive meniscus lens whose lens surface facing the image surface side is convex; and a fourth lens configured to have negative refractive power in the proximity of the optical axis but to have larger positive refractive power toward the periphery of the lens.